GB2504351A

GB2504351A - Method of controlling hybrid powertrain having an engine operating under rich combustion

Info

Publication number: GB2504351A
Application number: GB1213414.4A
Authority: GB
Inventors: Luca Scavone; Roberto Argolini
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2012-07-27
Filing date: 2012-07-27
Publication date: 2014-01-29
Also published as: GB201213414D0

Abstract

A method of controlling hybrid powertrain (100, fig 1) comprising a motor-generator electric unit (500) and an internal combustion engine (110), e.g. a diesel. When the internal combustion engine (110) operates under rich combustion conditions and at least a strategy 21, 22 requiring a torque fast transient response is active, the method verifies 23 if the conditions to actuate the motor-generator electric unit (500) are met, and if yes, the motor-generator electric unit (500) is activated 24 to rapidly increase or decrease the available torque to a drive shaft. The strategies 21, 22 which require a fast transient torque may include controlling gear shifting of an automatic transmission AT, traction control TC and control of driveline oscillations. Conditions to actuate the motor (500) may include a state of charge of a battery and batter power. Reference is also made to a hybrid powertrain configured to carry out the method and to a computer program comprising computer code which performs the method.

Description

METHOD OF CONTROLL/NG A HYBRID P0 WERTRA IN

DURING RICH COMBUSTION CONDITIONS

TECHNICAL FIELD

The present disclosure relates to a method of controlling a hybrid powertrain, for improving the achieved torque in fast transient, when the internal combustion engine operates under rich combustion conditions.

BACKGROUND

It is known that any motor vehicle is equipped with a powertrain, namely with a group of components and/or devices that are provided for generating mechanical power and for delivering it to the final drive of the motor vehicle, such as for example the drive wheels of a car.

A hybrid powertrain particularly comprises an internal combustion engine (ICE), such as for example a compression-ignition engine (Diesel engine) or a spark-ignition engine (gasoline or gas engine), and a motor-generator electric unit (MGU). The MGU can operate as an electric motor for assisting or replacing the ICE in propelling the motor vehicle, and can also operate as an electric generator, especially when the motor vehicle is braking, for charging an electrical energy storage device (battery) connected thereto.

Besides, the battery is provided for powering the MGU when it operates as electric motor.

The hybrid powertrain is controlled by an electronic control system according to a dedicated hybrid control strategy. During the traction of the motor vehicle, the hybrid control strategy provides for determining an overall value of mechanical power to be delivered to the wheels of the motor vehicle, for splitting this overall value in a first contributing value of mechanical power to be requested to the ICE and a second contributing value of mechanical power to be requested to the MGU, and then for operating the ICE and the MGU to deliver to the wheels of the motor vehicle the respective contributing value of mechanical power.

In greater details, the splitting of the above mentioned overall power value is conventionally optimized by determining, among the infinite couples of first and second contributing power values whose addition is equal to the overall power value, the couple that minimize the a predetermined polynomial function, usually referred as target function, which quantifies an overall power that is lost due to the operation of the hybrid powertrain, namely a quantity of power that has been supplied to the hybrid powertrain through the ICE fuel, but that has not been delivered to the final drive of the motor vehicle, for example because it has been dissipated due to specific aspect of the hybrid powertrain operation.

As a consequence of this optimization, the first contributing power value is always positive, whereas the second contributing power value may be either positive or negative. If the second contributing power value is positive, the MGU is operated as an electric motor that actually supplies mechanical power to the final drive. If the second contributing power value is negative, the MGU is operated as an electric generator that actually absorbs mechanical power from the final drive.

The fact that, being directly or indirectly connected to the ICE, the MGU can add or subtract torque to ICE, allows to face and solve a technical problem. In particular, the present technical problem arises, when the internal combustion engine operates under rich combustion conditions, e.g. during the regeneration of a lean NOx trap (LNT), and when a fast change of the delivered torque is required (for example, during gearshifting for automatic transmission, traction control intervention, driveline anti oscillating strategy).

As also known, the exhaust gas after-treatment systems of a Diesel engine can be provided, among other devices, with a Lean NOx Trap (LNT).

A Lean NOx Trap (LNT) is provided for trapping nitrogen oxides NOx contained in the exhaust gas and is located in the exhaust line A LNT is a catalytic device containing catalysts, such as Rhodium, Platinum and Palladium, and adsorbents, such as barium based elements, which provide active sites suitable for binding the nitrogen oxides (NOx) contained in the exhaust gas, in order to trap them within the device itself.

Lean NOx Traps (LNT) are subjected to periodic regeneration processes, whereby such regeneration processes are generally provided to release and reduce the trapped nitrogen oxides (NOx) from the LNT.

The LNT are operated cyclically, for example by switching the engine from lean-bum operation to operation whereby an excess amount of fuel is available, referred also as rich operation or regeneration phase. During normal operation of the engine, the NOx are stored on a catalytic surface. When the engine is switched to rich operation, the NOx stored on the adsorbent site react with the reductants in the exhaust gas and are desorbed and converted to nitrogen and ammonia, thereby regenerating the adsorbent site of the catalyst.

Therefore, LNT typical combustion modes require rich combustion (airlfuel ratio C stoichiometric air/fuel ratio): in those conditions, the engine final torque depends on both involved fluid quantities, air and fuel.

Since the air actuators (throttle valve, control of the variable geometry turbine, exhaust gas recirculation) are slower than the fuel ones (injectors), this means that the response of the engine, in rich combustion mode, is the same of the air system.

On the other side, the control of systems like automatic transmission, traction control or anti-oscillating system needs a fast reaction of the engine about the delivered torque. For diesel engine, normally operating under lean combustion mode, this is guarantee by the fact that injection can be moved fast, for gasoline engine this is guarantee by spark timing change. For diesel engine, whenever operating under rich combustion mode (e.g. during regeneration of the aftertreatment system) this cannot be anymore ensured.

Therefore a need exists for a method that allows to improve the achieved torque in fast transient, when the internal combustion engine operates under rich combustion conditions.

An object of an embodiment of the invention is to provide a method for increasing or decreasing the torque, available to the drive shaft, during fast transient conditions in a hybrid powertrain and with the thermal engine operating under rich combustion conditions Another object is to provide an apparatus which allows to perform the above method.

These objects are achieved by a method, by an apparatus, by an engine, by a computer program and computer program product, and by an electromagnetic signal having the features recited in the independent claims.

The dependent claims delineate preferred and/or especially advantageous aspects.

SUMMARY

An embodiment of the disclosure provides a method of controlling a hybrid powertrain comprising a motor-generator electric unit and an internal combustion engine, when the internal combustion engine operates under rich combustion conditions and at least a strategy requiring a torque fast transient response is active, the method comprising the following steps: -verifying if the conditions to actuate the motor-generator electric unit are met, and if yes, -actuating the motor-generator electric unit, to rapidly increase or decrease the available torque to the drive shaft Consequently, an apparatus is disclosed for controlling a hybrid power-train, the apparatus comprising: -means for verifying if the conditions to actuate the motor-generator electric unit are met, and if yes, -means for actuating the motor-generator electric unit, to rapidly increase or decrease the available torque to the drive shaft.

An advantage of this embodiment is that it allows to improve the achieved torque in fast transient and to meet powertrain electrical interface requirements also during rich mode intervention.

According to another embodiment of the invention, said strategy requiring a fast transient torque is a control of a gear-shifting for automatic transmissions.

An advantage of this embodiment is that the method provides a fast reaction of the engine about the delivered torque during gear-shifting for automatic transmissions According to a further embodiment of the invention said strategy requiring a fast transient torque is a traction control.

An advantage of this embodiment is that the method provides a fast reaction of the engine about the delivered torque during traction control operations.

According to a still further embodiment, said strategy requiring a fast transient torque is a control of the driveline oscillations.

An advantage of this embodiment is that the method provides a fast reaction of the engine about the delivered torque during the control of the driveline oscillations.

According to another embodiment of the invention, the conditions to actuate the motor-generator electric unit are the state of charge of the batteries and the battery power.

An advantage of this embodiment is that it allows to improve the integration between the torque management and the MGU management.

According to still another embodiment, the invention relates to a hybrid powertrain comprising a motor-generator electric unit, an internal combustion engine, the hybrid powertrain comprising an electronic control unit configured for carrying out the above method.

An advantage of this embodiment is that it allows to reduce the system complexity of a hybrid powertrain and to pursuit integration.

The method according to one of its aspects can be carried out with the help of a computer program comprising a program-code for carrying out all the steps of the method described above, and in the form of computer program product comprising the computer program.

The computer program product can be embodied as a control apparatus for an internal combustion engine, comprising an Electronic Control Unit (ECU), a data carrier associated to the ECU, and the computer program stored in a data carrier, so that the control apparatus defines the embodiments described in the same way as the method. In this case, when the control apparatus executes the computer program all the steps of the method described above are carried out.

The method according to a further aspect can be also embodied as an electromagnetic signal, said signal being modulated to carry a sequence of data bits which represents a computer program to carry out all steps of the method.

A still further aspect of the disclosure provides an internal combustion engine specially arranged for carrying out the method claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 schematically represents a hybrid powertrain of a motor vehicle.

Figure 2 shows in more details an internal combustion engine belonging to the hybrid powertrain of figure 1.

Figure 3 is a section A-A of the internal combustion engine of figure 2.

B

Figure 4 is a graph depicting the torque behavior in fast transient, with the thermal engine running under rich combustion conditions.

Figure 5 is a flowchart of a method for increasing or decreasing the available torque during fast transient, according to the invention.

DETAILED DESCRIPTION S THE DRAWINGS

Some embodiments may include a motor vehicle's mild hybrid powertrain 100, as shown in Figures 1, that comprises an internal combustion engine (ICE) 110, in this example a diesel engine, a motor-generator electric unit (MGU) 500, an electric energy storage device (battery) 600 electrically connected to the MGU 500, and an electronic control unit (ECU) 450 in communication with a memory system 460.

As shown in Figures 2 and 3, the ICE 110 has an engine block 120 defining at least one cylinder 125 having a piston 140 coupled to rotate a crankshaft 145. A cylinder head 130 cooperates with the piston 140 to define a combustion chamber 150. A fuel and air mixture (not shown) is disposed in the combustion chamber 150 and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston 140. The fuel is provided by at least one fuel injector 160 and the air through at least one intake port 210. The fuel is provided at high pressure to the fuel injector 160 from a fuel rail 170 in fluid communication with a high pressure fuel pump 180 that increase the pressure of the fuel received a fuel source 190. Each of the cylinders 125 has at least two valves 215, actuated by a camshaft 135 rotating in time with the crankshaft 145. The valves 215 selectively allow air into the combustion chamber 150 from the port 210 and alternately allow exhaust gases to exit through a port 220. In some examples, a cam phaser 155 may selectively vary the timing between the camshaft 135 and the crankshaft 145.

The air may be distributed to the air intake port(s) 210 through an intake manifold 200.

An air intake duct 205 may provide air from the ambient environment to the intake manifold 200. In other embodiments1 a throttle body 330 may be provided to regulate the flow of air into the manifold 200. In still other embodiments, a forced air system such as a turbocharger 230, having a compressor 240 rotationally coupled to a turbine 250, may be provided. Rotation of the compressor 240 increases the pressure and temperature of the air in the duct 205 and manifold 200. An intercooler 260 disposed in the duct 205 may reduce the temperature of the air. The turbine 250 rotates by receiving exhaust gases from an exhaust manifold 225 that directs exhaust gases from the exhaust ports 220 and through a series of vanes prior to expansion through the turbine 250. The exhaust gases exit the turbine 250 and are directed into an exhaust system 270. This example shows a variable geometry turbine (JOT) with a VGT actuator 290 arranged to move the vanes to alter the flow of the exhaust gases through the turbine 250. In other embodiments, the turbocharger 230 may be fixed geometry and/cr include a waste gate.

The exhaust system 270 may include an exhaust pipe 275 having one or more exhaust aftertreatment devices 280. The aftertreatment devices may be any device configured to change the composition of the exhaust gases. Some examples of aftertreatment devices 280 include, but are not limited to, catalytic converters (two and three way), oxidation catalysts, lean NOx traps, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems, and particulate filters. Other embodiments may include an exhaust gas recirculation (EGR) system 300 coupled between the exhaust manifold 225 and the intake manifold 200. The EGR system 300 may include an EGR cooler 310 to reduce the temperature of the exhaust gases in the EGR system 300. An EGR valve 320 regulates a flow of exhaust gases in the EGR system 300.

The MGU 500 is an electric machine, namely an electro-mechanical energy converter, which is able either to convert electricity supplied by the battery 600 into mechanical power (i.e., to operate as an electric motor) or to convert mechanical power into electricity that charges the battery 600 (i.e., to operate as electric generator). In greater details, the MGLJ 500 may comprise a rotor, which is arranged to rotate with respect to a stator, in order to generate or respectively receive the mechanical power. The rotor may comprise means to generate a magnetic field and the stator may comprise electric windings connected to the battery 600, or vice versa. If the MGU 500 operates as electric motor, the battery 600 supplies electric currents in the electric windings, which interact with the magnetic field to set the rotor in rotation. Conversely, when the MGU 500 operates as electric generator, the rotation of the rotor causes a relative movement of the electric wiring in the magnetic field, which generates electrical currents in the electric windings. The MGU 500 may be of any known type, for example a permanent magnet machine, a brushed machine or an induction machine. The MGU 500 may also be either an asynchronous machine or a synchronous machine.

The rotor of the MGU 500 may comprise a coaxial shaft 505, which is mechanically is connected with other components of the hybrid powertrain 100, so as to be able to deliver or receive mechanical power to and from the final drive of the motor vehicle. In this way, operating as an electric motor, the MGU 500 can assist or replace the ICE 110 in propelling the motor vehicle, whereas operating as an electric generator, especially when the motor vehicle is braking, the MGU 500 can charge the battery 600. In the present example, the MGU shaft 505 is connected with the ICE crankshaft 145 through a transmission belt 510, similarly to a conventional alternator starter. In order to switch between the motor operating mode and the generator operating mode, the MGU 500 may be equipped with an appropriate internal control system.

The automotive system 100 may further include an electronic control unit (ECU) 450 in communication with one or more sensors and/or devices associated with the ICE 110 and equipped with a memory system 460. The ECU 450 may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the ICE 110 and the MGU 500.

Turning now to the ECU 450, this apparatus may include a digital central processing unit (CPU) in communication with the memory system 460 and an interface bus. The memory system 460 may include various storage types including optical storage, magnetic storage, solid state storage, and other non-volatile memory. The interface bus may be configured to send, receive, and modulate analog and/or digital signals to/from the various sensors and control devices. The CPU is configured to execute instructions stored as a program in the memory system 460, and send and receive signals to/from the interface bus. The program may embody the methods disclosed herein, allowing the CPU to carryout out the steps of such methods and control the ICE 110 and the MGU 500.

In order to carry out these methods, the ECU 450 is in communication with one or more sensors and/or devices associated with the ICE 110, the MGU 500 and the battery 600.

The ECU 450 may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the ICE 110, the MGU 500 and the battery 600. The sensors include, but are not limited to, a mass airflow and temperature sensor 340, a manifold pressure and temperature sensor 350, a combustion pressure sensor 360, coolant temperature sensor 385, oil temperature sensor 385, a fuel rail pressure sensor 400, a camshaft position sensor 410, a crankshaft position sensor 420, exhaust pressure and temperature sensors 430, an EGR temperature sensor 440, a sensor 445 of a position of an accelerator pedal 446, and a measuring circuit 605 capable of sensing the state of charge of the battery 600.

Furthermore, the ECU 450 may generate output signals to various control devices that are arranged to control the operation of the ICE 110 and the MGU 500, including, but not limited to, the fuel injectors 160, the throttle body 330, the EGR Valve 320, the VGT actuator 290, the cam phaser 155, and the above mentioned internal control system of the MGU 500. Note, dashed lines are used to indicate communication between the ECU 450 and the various sensors and devices, but some are omitted for clarity.

The method according to the present invention is based on the fact that the electric motor 500 of the hybrid powertrain, being directly or indirectly connected to the ICE 110, could contribute to the internal combustion engine torque during conditions of fast transient torque request, with the thermal engine operating under rich combustion conditions.

This rich combustion conditions are required, as an example, during lean NOx trap regeneration. In fact, during normal condition with the thermal engine operating under lean combustion conditions, NOx are stored in LNT as Ba(N03)2. When the trap is full the engine is forced to run with air/fuel ratios lower than 1, to produce high quantity of CO and H2, which react with NOx stored and produce N2, H20 and C02. This means that the response of the engine, in rich combustion mode, is the same of the air system.

In fact while in lean combustion conditions the air actuators (EGR, variable geometry turbine actuator, throttle valve) which are usually relatively slow and have low influence on the final produced torque and, on the contrary, the fuel actuators (mainly injectors), which are very fast, are the principal parameter influencing the final torque, under rich conditions the air actuators have the same weight of the fuel actuators in producing the engine torque. Fig. 4 shows several examples of transient torque behavior under rich combustion conditions. In the different performed tests (1 to 8), the difference between them is the final torque value to be achieved after the transient step.

On the other side, the control of systems like automatic transmission, traction control, anti-oscillating system needs a fast reaction of the engine about the delivered torque. For conventional diesel engine, operating under lean combustion conditions, this is guarantee by the fact that injection can be moved fast, for gasoline engine this is guarantee by spark timing change. For diesel engine with rich combustion this cannot be anymore ensured and the torque behaviors as in Fig. 4 do not fulfill the requirements available for such systems. For example, the specification, known as powertrain electrical interface (PTEI), defines a fast transient response when the output actuation delay is < l5ms, the maximum response time is equal to 150 ms and the minimum response rate is 600 Nm/s.

Using a hybrid system, it is possible to obtain a faster transient torque by means of an electric torque which can be supplied by the electric motor 500. 14

In fact, turning to the flowchart in Fig. 5, more in detail, the method for improving the fast transient torque achievement, when 20 the internal combustion engine operates under rich combustion conditions and at least a strategy 21, 22 requiring a fast transient torque is active, starts verifying 23 if the conditions to actuate the motor-generator electric unit (500) are met and, if yes, then actuate 24 the motor-generator electric unit 500, to increase or decrease the available torque to the drive shaft, in other words, to fill the gap and reach a faster transient torque behavior. Said strategies 21, 22 requiring a fast transient torque are, for example, the control of a gear-shifting for automatic transmissions, the traction control and the control of the driveline oscillations. For example, the control of a gear shifting for automating transmission will require either a fast increasing of the torque (upshift) or a fast decreasing of the torque (downshift). The same happens for the traction control: the activation of the traction control will require a fast torque reduction, while the deactivation will require a fast torque increasing.

Advantageously, the conditions to actuate the motor-generator electric unit 500 are the state of charge of the batteries and the battery power. In case such conditions are not satisfied, the MGU 500 will not be actuated and the method, following the path "no" as in Fig. 5, will look for the next condition requiring a fast transient torque achievement.

While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.

REFERENCE NUMBERS

1 torque behaviour curve 2 torque behaviour curve 3 torque behaviour curve 4 torque behaviour curve torque behaviour curve 6 torque behaviour curve 7 torque behaviour curve 8 torque behaviour curve 20 block 21 block 22 block 23 block 24 block 100 hybrid powertrain internal combustion engine engine block cylinder cylinder head 135 camshaft piston crankshaft combustion chamber cam phaser 160 fuel injector fuel rail fuel pump fuel source intake manifold 205 air intake pipe 210 intake port 215 valves 220 exhaust port 225 exhaust manifold 230 turbocharger 240 compressor 250 turbine 260 intercooler 270 exhaust system 275 exhaust pipe 280 DOC 281 LNT 282 DPF 290 VGT actuator 300 exhaust gas recirculation system 305 EGR conduit 310 EGR cooler 320 EGR valve 330 throttle body 340 mass airflow and temperature sensor 350 manifold pressure and temperature sensor 360 in-cylinder pressure sensor 380 coolant temperature sensor 385 oil temperature sensor 400 fuel rail pressure sensor 410 camshaft position sensor 420 crankshaft position sensor 430 exhaust pressure and temperature sensors 440 EGR temperature sensor 445 accelerator pedal position sensor 446 accelerator pedal 450 ECU 460 memory system 500 motor-generator electric unit 505 MGU shaft 510 transmission belt 600 battery 605 measuring circuit

Claims

CLAIMS1. Method of controlling a hybrid powertrain (100) comprising a motor-generator electric unit (500) and an internal combustion engine (110), when (20) the internal combustion engine operates under rich combustion conditions and at least a strategy (21, 22) requiring a torque fast transient response is active, the method comprising the following steps: -verifying (23) if the conditions to actuate the motor-generator electric unit (500) are met, and if yes, -actuating (24) the motor-generator electric unit (500), to rapidly increase or decrease the available torque to the drive shaft.
2. Method according to claim 1, wherein said strategy (21) requiring a fast transient torque is a control of a gear-shifting for automatic transmissions.
3. Method according to claim 1, wherein said strategy (21) requiring a fast transient torque is a traction control.
4. Method according to claim 1. wherein said strategy (22) requiring a fast transient torque is a control of the driveline oscillations.
5. Method according to one of the previous claims, wherein the conditions to actuate the motor-generator electric unit (500) are the state of charge of the batteries (600) and the battery power.
6. Hybrid powertrain (100) comprising a motor-generator electric unit (500), a plurality of batteries (600), an internal combustion engine (110), the hybrid powertrain (100) comprising an electronic control unit (450) configured for carrying out the method according to claims 1-5.
7. Hybrid powertrain (100) according to claim 6, wherein said internal combustion engine is a diesel engine.
8. A computer program comprising a computer-code suitable for performing the method according to any of the claims 1-5.
9. Computer program product on which the computer program according to claim 8 is stored.
10. Control apparatus for an internal combustion engine, comprising an Electronic Control Unit (450), a data carrier (40) associated to the Electronic Control Unit (450) and a computer program according to claim 8 stored in a memory system (460).
11. An electromagnetic signal modulated as a carrier for a sequence of data bits representing the computer program according to claim B.